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A2 Biology > F214: Communication And Homeostasis > Flashcards

F214: Communication And Homeostasis Flashcards

0
Q

What is a response?

A

Any change in behaviour or physiology as a result of a change in the environment.

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1
Q

What is a stimulus?

A

Any change in the environment that causes a response.

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2
Q

Why is a multicellular organism more efficient than a single celled organism?

A

It’s cells can be differentiated and have specific jobs it’s adapted for.

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3
Q

What does a good communication system do?

A

Cover the whole body.
Enable cells to communicate with each other.
Enable specific communication.
Enable rapid communication.
Enable both short an long term responses.

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4
Q

What are the two systems if communication in cell signalling?

A

Neuronal system:
Interconnected network of neurones that signal across synapse junctions. Very quick response.

Hormonal system:
Uses the blood.
Cells in an endocrine organ release hormones directly into the blood, which is carried over the body, but is only recognised by target cells.
Long term responses.

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5
Q

What is homeostasis?

A

The maintenance of the internal environment in a constant state despite external changes.

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6
Q

What are example of condition that must be maintained in the body?

A 
Temperature.
Blood glucose concentration.
Blood salt concentration. 
Water potential of the blood. 
Blood pressure.
CO2 concentration.
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7
Q

What is the general process of maintaining a constant environment.

A

A change must be detected.
The change must be signalled to other cells.
A response to reverse the change must occur.

(Negative feedback)

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8
Q

What is negative feedback?

A

A process that brings about the reversal of any change in conditions.
Ensures an optimum state is maintained, any change in the internal environment is returned to it’s original state.
It is essential for homeostasis.

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9
Q

What structures are needed for negative feedback to work?

A

Sensory receptors: internal monitors that send a message to other cells when a change is detected.
eg temperature receptors or glucose conc receptors.

A communication system: nervous or hormone system. They are used to transmit messages from receptor cells to effector cells.

Effector cells: bring about a response that reverses the change detected by the receptor cells.
Eg liver or muscles cells.

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10
Q

What is positive feedback?

A

A process that increases any change detected by the receptors.
It is harmful and does not lead to homeostasis.

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11
Q

Describe beneficial accounts of positive feedback.

A

At the end of pregnancy, positive feedback brings about the dilation of the cervix.
As it begins to stretch the change is signalled to the anterior pituitary gland, stimulating it to produce oxytocin.
Oxytocin increases the contractions, which increases the secretion of more oxytocin.

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12
Q

What is an ectotherm?

A

An organism that relies on external sources of heat to regulate it body temperature.

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13
Q

What are advantages of being an ectotherm?

A

Use less energy and food in respiration.
Need to find less food so can survive for longer without it.
A greater proportion of energy is used for growth.

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14
Q

What are disadvantages of being an ectotherm?

A

They are less active in cooler temperatures, as may need to warm up in the morning before they can be active.
This increases the risk of predation.

May never be capable of activity during the winter as they never warm up sufficiently.
Thus they must have stores of energy to survive without eating.

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15
Q

How do ectotherms respond to temperature changes?

A

If it is too cold it will move to decrease absorption of heat an increase heat loss to the environment.

If it is too hot it will increase absorption of heat from the environment, eg basking in the sun.

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16
Q

Give examples of ectotherms regulating their body temperature.

A 
Exposing body to the sun.
Orientating body to/from the sun.
Hide in burrow.
Alter body shape.
Increase breathing movements to evaporate more water.
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17
Q

What is an endotherm?

A

An organism that can use internal sources of heat to maintain it’s body temperature.

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18
Q

What are advantages of endothermy?

A

Regardless of external temperature a constant body temperature is maintained.
Activity is possible when external temperature are cold.
Ability to inhabit colder parts of the planet.

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19
Q

What are the disadvantages of endothermy?

A

A significant part of energy intake is used to maintain body temperature.
More food required.
Less of the energy from food is used for growth, so more good a needed for growth.

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20
Q

Describe physiological mechanisms to maintain body temperature in endotherms.

A

Peripheral skin thermite rotors are stimulated by a decrease in external temp.

Vasoconstriction of arterioles to reduce heat loss by conduction.

Increased respiration to generate heat energy.

Release of adrenaline.

Shivering to generate heat energy.

Erector pulli muscles raise hair to trap air and hear.

Swearing or panting is reduced.

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21
Q

Where is the temperature of the blood monitored?

A

Hypothalamus.

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22
Q

If the core temperature is too low how does the hypothalamus respond?

A

Increased rate of metabolism to release more heat from exergonic reactions.
Extra muscular contraction releases heat.
Decreases loss of heat to environment.

Vice versa for increase in temp.
Negative feedback.

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23
Q

What are the peripheral temperature teceptors?

A

In the skin and alert the hypothalamus that the extremities, eg fingers, are changing in temperature and to initiate behavioural mechanism to maintain body temperature.

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24
What are exergonic reactions?
Release energy in the form of heat.
25
What is a generator potential?
A small depolarisation caused by sodium ions entering the cell.
26
What I an action potential?
Achieved when the membrane is depolarised to a value of about +40mv. All or nothing. Membrane depolarised and reaches a threshold level, then lots of sodium ions enter the axon and an action potential is reached.
27
What are sensory receptors?
Specialised cells that can detect changes in our surroundings. They are transducers, they convert one form of energy to another.
28
What are neurones?
Nerve cells.
29
What do nerve cell membranes transport in and out of the cell? How does this affect the cell?
3 Sodium ions out of the cell. 2 Potassium ions into the cell. More sodium out than potassium in. Polarises the cell membrane as inside is negatively charged.
30
What is a polarised membrane?
Has a potential difference across it, this is it's resting potential.
31
What Is depolarisation?
Loss of polarisation across the membrane, sodium ions enter the cell and make it less negative compared to the outside.
32
How does the size of the stimulus effect the potential?
Larger stimulus opens more gated sodium channels and generators a larger potential.
33
What are the types of neurones?
Sensory neurones: carry the action potential from sensory receptor to the central nervous system. Motor neurones: carry an action potential from the CNS to an effector such as a muscle or gland. Relay neurones: connect sensory and motor neurones.
34
How are neurones adapted torque function?
Very long to transmit the AP over a long distance. Cell surface has many gated ion channels. Na/K ion pumps to actively transport Na+ out and K+ in. Maintain a p.d. Across their membrane. Surrounded by a Myelin sheath that insulates it from nearby cells. Mitochondria and ribosomes. Dendrites connected to other neurones.
35
Learn how to draw a neurone.
Page 13.
36
What is the resting potential? | Describe the cell at this time.
-60mv inside the cell compared to the outside. Potential difference when the neurone is at rest. Gated Na ion channels are closed, the pumps are open using ATP to transport 3Na out and 2K in. Some K are open and some diffuse out.
37
Describe the permeability of the neurone cell membrane.
More permeable to potassium ions an many diffuse out once pumped in.
38
What is a voltage gated channel?
Channels in the cell membrane that allow the passage of ions or charge particles. They respond to depolarisations of the membrane.
39
What is the threshold potential?
About -50mv. | The depolarisation of the membrane must reach this to create an action potential.
40
Describe the stages of an action potential.
Starts at it's resting state. -60mv. Sodium ion channels open and ions diffuse into the cell. The membrane depolarises and reaches a threshold value of -50mv. Voltage gated Na ion channels open and more Na ions flood in. The potential difference reaches +40mv. Na ion channels close and K channels open. K ions diffuse out and bring the potential difference down. REPOLARISATION. The potential difference overshoots slightly, making the cell HYPERPOLARISED. Original potential difference is resorted. Resting potential. Refractory period.
41
What is the refractory period?
After the action potential has been transmitted, the neurone can't be stimulated again. Allows the cell to recover and ensure the action potential is transmitted in one direction.
42
What is a local current?
The movement of ions along the neurone. Caused by an increase in concentration at one point, which causes diffusion away from the region of higher concentration.
43
Explain local currents in detail.
When an action potential occurs the Na ion channels open at a point along the neurone. Na ions diffuse across the membrane from the region of high concentration outside the neurone into the neurone. This upsets the balance of ions in the cell. The Concentration of Na ions increases at that point. The Na ions diffuse sideways down a concentration gradient. This movement of charged particles is a local current.
44
How do voltage gated sodium ion channels contribute to action potentials?
They open when the potential difference is reduced, when sodium ions diffuse sideways and reach a new voltage gate it will open. This lets Na ions flow in and the local current continues along the neurone.
45
What does Saltatory mean?
Jumping conduction, it is how the action potential appears to jump from one node of ranvier to the next.
46
Describe the myelin sheath.
An insulating fatty later which ion cannot diffuse through. Made up of Schwann cells. There are gaps called the nodes of ranvier. Ionic exchanges that cause action potentials only occur at the nodes of ranvier.
47
What are the advantages of Saltatory conduction/myelination?
Speed up the transmission of action potentials by not allowing ions to diffuse our between the nodes of ranvier. No interference from other cells.
48
What is a neurotransmitter?
A chemical that diffuses across the cleft of the synapse to transmit a signal to the post synaptic neurone.
49
What are cholinergic synapses?
Synapses that use acetylcholine as a neurotransmitter.
50
What is the synaptic knob?
A swelling at the end of the presumptive neurone.
51
What is a synpase?
A junction between multiple neurones.
52
How Is the synaptic knob specialised?
Many mitochondria as ATP is needed. Lots of smooth endo plastic reticulum to produce lipids to make vesicles. Vesicles of acetylcholine, the neurotransmitter. Voltage gated Na ion channels in the membrane.
53
Describe the postsynaptic membrane.
Contains specialised Na ion channels that respond to the neurotransmitter. Receptors are complementary, when acetylcholine binds to the two receptors the Na ion channel opens.
54
Describe the stages of a transmission across the synpase.
An action potential arrives at the synaptic knob. The voltage gated Na ion channels open. Na ions diffuse into the synaptic knob. Na ions cause the synaptic vesicles to move and fuse with the presumptive membrane. Acetylcholine is released by exocytosis, and diffuses across the cleft. Binds to receptor sites on Na ion channels in the postsynaptic membrane. Complementary. Na ion channels open and Na ions diffuse across the postsynaptic membrane into the postsynaptic neurone. A generator potential is created. If sufficient or multiple gps are made the threshold potential is passed. This creates a new action potential.
55
What is acetylcholinesterase and it's function?
Enzyme in the synaptic cleft that hydrolysed acetylcholine to ethanoic acid and choline. This stops transmission of signals so no more action potentials are created. The ethanoic acid and choline re enter the synaptic knob by diffusion and are recombined to form acetylcholine using ATP. Then stored in vesicles.
56
How are action potentials said to be all or nothing?
Either conducts one or doesn't, depending if it reaches the threshold potential. All action potentials are the same magnitude: +40mv.
57
What is summation?
Several small potential changes can combine to produce one larger change in the potential difference across the membrane.
58
What are the roles of synapses in the nervous system?
Ensure signals are transmitted in the correct direction, only the presynaptic knob contains acetylcholine. One pre to several post or vice versa. Eg One elicits a response while other goes to brain. Or same response from many. Filter out low level stimulus since many vesicles of acetylcholine must pass to the post in order to reach threshold potential, a low level will only make a couple pass. Summation, persistent low level. Acclimatisation, the synapse runs out of vesicles after repeated stimulation. Avoids overstimulation/damage and we no longer respond.
59
How do we determine the intensity of signals?
The frequency of transmissions, as all aps have the same magnitude.
60
What are the functions of myelinated and non myelinated neurones?
Myelinated carry over long distances from sensory receptors to the CNS or from the the CNS to effectors. Non myelinated carry over short distances where speed is not so important.
61
What are hormones?
Molecules that are released by endocrine glands directly into the blood. Carry a signal from the endocrine gland to a specific target organ or tissue.
62
What is an endocrine gland?
A gland that secretes hormones directly into the blood, they contain no ducts.
63
What is an exocrine gland?
A gland that secretes molecules into a duct that carries the molecule to where they are used. Do not secrete hormones.
64
What are the target cells?
Those that possess a specific receptor on their cell mebrane. Complementary shape to that on the hormone molecule. Many similar cells from a tissue.
65
What is adenyl Cyclase?
An enzyme associated with the receptor for many hormones, including adrenaline. Found inside the cell surface membrane.
66
What are the types of hormones?
Protein/peptide hormones. Eg adrenaline. Not soluble to the phospholipid bilayer and do not enter the cell. Steroid hormones. Eg sex hormones. Enter the cell and directly effect the DNA of the cell.
67
Describe the action of adrenaline.
An amino acid derivative so cannot enter the cell directly. Complementary receptor on surface of cell membrane. Adrenaline binds to the receptor, and is the first messenger. This activates adenyl Cyclase inside the cell membrane to be released. AC concerts ATP to cyclic AMP (cAMP) cAMP is the second messenger and activates enzyme action inside the cell.
68
What are the adrenal glands?
Found above the kidneys. | Divided into the medulla and the cortex regions.
69
Describe the adrenal medulla.
Centre of the adrenal glands. | Cells here manufacture and release adrenaline.
70
Describe the effects of adrenaline.
Increase stroke volume of the heart. Increase heart rate. Increase vasoconstriction to increase blood pressure. Dilate pupils. Stimulate conversion of glycogen to glucose.
71
Describe the adrenal cortex.
Uses cholesterol to produce steroid hormones. The mineralocorticoids help control the concentrations of Na/K in the blood. The glucocorticoids control the metabolism of carbohydrates and proteins in the liver.
72
Why is the pancreas unusual?
Has both endocrine and exocrine functions.
73
Describe the exocrine function of the pancreas.
Releases digestive enzymes. The cells secrete the enzymes into tiny tubules that join up to make the pancreatic duct. The pancreatic duct contains fluid containing the enzymes, amylase, trypsinogen (an inactive protease) and lipase. Also contains Na hydrogen carbonate to make it alkaline and neutralise the acidic contents of the digestive system.
74
What is the pancreatic duct?
A tube that collects all the secretions from the exocrine cells in the pancreas and carries the fluid to the small intestine.
75
What are the islets of langerhans?
Small patches of tissue in the pancreas that have an endocrine function.
76
Deprive the cells found in the islets of langerhans.
Alpha: secrete glucagon. Beta: secrete insulin. Both hormones.
77
What are the uses of insulin and glucagon?
Insulin: casuals blood glucose levels to decrease Glucagon: causes blood glucose levels to rise.
78
What are the target cells to alter blood glucose levels? | How does it do this?
``` Hepatocytes (liver cells) Muscle cells (only insulin) ``` Bind to receptors on membrane surface, activates adenyl Cyclase inside the cell which converts ATP to cAMP etc.
79
What are the effects of insulin on a cell?
Blood glucose too high: More glucose channels are placed into the surface membrane. More glucose enters the cell. Glucose is converted to glycogen for storage (glycogenesis) More glucose used in respiration.
80
What are the effects of glucagon on a cell?
Blood glucose too low: Conversion of glycogen to glucose (glycogenolysis). More fatty acids used in respiration. More glucose made by conversion from amino acids/fats (gluconeogenesis)
81
Describe the stages when there is a rise in blood glucose concentration.
Detected by B cells in islets of langerhans. B cells secrete insulin into blood. Insulin detected by receptors on liver and muscles cells. Liver and muscle cells remove glucose from blood and convert glucose to glycogen. Blood glucose contraction decreases.
82
Describe the stages when there is a fall in blood glucose concentration.
Detected by A cells in islets. A cells secrete glucagon into blood. Glucagon detected by receptors on liver cells. Liver cells convert glycogen to glucose and release glucose into the blood. Glucose concentration increases.
83
What is the disease in which blood glucose levels cannot be controlled effectively?
Diabetes mellitus.
84
What is hyperglycaemia?
The state in which the blood glucose concentration is too high.
85
Describe the control of insulin secretion?
Cell membrane of B cells contain Na/K ion channels. K usually open and Na closed, K ions flow out, rest potential -70mv. When glucose concentrations increase they diffuse into the cell. The glucose is used to make ATP. This ATP causes the K channels to close. K ions cannot diffuse out and the cell becomes less negative. This change in p.d. Opens Na ion channels. Na ions enter the cell and cause the secretion of insulin by making the vesicles containing insulin move to the cell surface membrane and fuse with it, releasing insulin by exocytosis.
86
How are blood glucose levels controlled?
Negative feedback.
87
What is hypoglycaemia?
The state in which the blood glucose concentration is too low.
88
Describe type I diabetes.
Insulin dependent. Starts in childhood. Body's own immune system attacks the B cells and destroys them. Cannot manufacture insulin as a result, or store excess glucose as glycogen.
89
What is type II diabetes?
Non insulin dependent. Can produce insulin but is no longer responsive to it. Decline in receptors or level of insulin secreted by B cells.
90
What factors bring about the onset of type II diabetes?
Obesity. High sugar diet. Family history.
91
How can diabetes be treated?
Type I: Insulin injections, blood glucose levels are monitored and the correct dose is applied. Type II: Controlled diet, can be supplemented by insulin injections. Match carbohydrate intake and usage. Genetically engineered insulin. Stem cells grown into an cells.
92
What Is the cell metabolism?
The result of all the chemical reactions taking place in the cytoplasm.
93
What is myogenic muscle tissue?
Muscle tissue that can initiate it's own contractions.
94
How does the heart adapt to supply more oxygen and glucose?
Increase in heart rate. Increase in strength of contractions. Increased stroke volume (vol per beat).
95
What is the medulla oblongata?
Found at the base of the brain, region of the brain that coordinates the unconscious functions of the body, eg heart rate.
96
What factors affect heart rate?
Page 28/29 for more. Movement of the limbs is detected by stretch receptors in muscles, send messages for more O2. Muscles produce CO2 when we excercise, this can react with water in the blood plasma and decrease pH. Detected by chemoreceptors. Adrenaline.
97
What is the cardiovascular centre?
A specific region of the medulla oblongata that recovers sensory inputs about levels of physical activity, CO2 conc in the blood and blood pressure. It sends nerve impulses to the SAN in the heart to alter the frequency of excitation waves.
98
Describe the structure of the heart.
Sino atrial node is the myogenic pacemaker, which travels as a wave of excitation over the atria walls through the atrioventricular node and down the Purkyne fibres to the ventricles, causing them to contract. Heart is supplied nerves from the medulla oblongata, which connect to the SAN.

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